Kisangani, a city of some 2m people at the very heart of Africa, is maybe the world’s most isolated big city. This is where the 1,200 kilometres of the Congo river ends, before bending south at the rapids that become the Lualaba river. It is where, 150 years ago, Henry Morton Stanley pushed through with his retinue of soldiers and porters, crossing from Indian Ocean to Atlantic for the first time. These days, in one direction, it is only slightly more accessible. West towards Kinshasa, Congo’s capital, the trip is a two-week journey on a barge huddling from the rain under plastic canopies. In the other direction, towards Kampala, Uganda’s capital, it is a three-day bumpy drive on roads infested with bandits.

Yet even here, under the thick canopy of rainforest, surrounded by derelict colonial buildings, the internet is opening the world up to people. One of the first people I met on arriving in Kisangani was Anderson Ngbado Ndabahweje, a 20-year-old student who I enlisted to help me translate. Anderson had never left Kisangani, a city in which almost nobody speaks English, and yet he spoke it remarkably fluently, with an American way of dropping his Ts. He would say things like “I godda learn to do dat” or “jus’ led me ged a glass of wader”, proudly drawling like a native speaker.

Anderson had decided to learn English because of his church – the result of a previous wave of globalisation in Kisangani. It was founded in the 1950s by William M Branham, a pastor from Kentucky. “Mr William was saving the world”, Anderson explained to me earnestly, “and I wish also to save the world.” For this, he had to be able to understand English, the language Branham preached in, but at his church, they had only poor French translations of his speeches. “French is one of my mother tongues,” he told me, adding that it was nothing to boast about here.

So Anderson turned to YouTube. This was not easy, because a gigabyte of data in Congo costs $10 – a fortune for most Congolese. But by sitting up after midnight, he could get off-peak internet for far less. On his ancient, battered Chinese smartphone, he showed me instructional videos he had downloaded about how to conjugate verbs, old American movies (“Coming to America” was a favourite), and speeches by Barack Obama. It was Obama who taught him to drop his Ts. “I heard him say this expression ‘gotta’. It was so complicated to me. I felt I had to learn to speak all over again.”

Some of what Anderson said made me cringe. “White people are so great at technology”, he told me, nodding solemnly. Belgian colonialists had “built everything good in Congo” and, he reckoned, independence had been a disaster. But in general, he was inspiring. This young man, with access to almost nothing but a smartphone, had learned how to access an entire world beyond it. In this crumbling, overgrown city a thousand kilometres away from any international airport, we were able to communicate directly, because he wanted to learn English and the internet made it possible.

But still, he’s stuck. Anderson’s dearest dream is to use his English to improve the lot of his fellow Congolese. But he can barely use it to make a living. In Kisangani, English is a rare skill but also a useless one. There are no big businesses here; the factories that were built in the Belgian era lie derelict. Not many NGOs or aid agencies have operations here; few journalists or researchers pass through. To use his English, Anderson will probably have to go to Uganda (and there it won’t be rare), or else to Goma, a big city on the Rwandan border where it might be useful translating for the hordes of people coming to understand Congo’s wars.

And that, ultimately, is both the glorious and the sad thing about the internet in some parts of Africa. In a place like Kisangani, some of the poorest and most isolated people on the planet can, through their smartphones, learn about things only the richest would have known about even a generation ago. Yet at the end of it, they are still stuck in Kisangani. How frustrating it must be to have the world revealed to you through a glowing portal in your hand, but never to be able to step through it?

Of course, plenty of Africans are trying to get through. From Congo, getting to Europe is at best a dream; getting even to Kinshasa is a journey of weeks. But from Nigeria, Senegal, Ivory Coast and elsewhere, thousands of young men are risking their lives to cross desert and sea, in the hope of reaching Italy. How many of them are inspired by what they see on their phones? For all the promise of the internet, if you don’t have the right passport the world can sometimes seem smaller than ever.